This invention relates to a layer or film to protect underlying functional coating layer(s) or film(s) and, in particular, to a sputter coated silicon oxynitride protective layer to protect underlying low emissivity coating film(s).
Vacuum deposited low emissivity (xe2x80x9cLow-Exe2x80x9d) coating stacks usually consist of the following general layer sequence: S/(D1/M/P/D2)R where:
S is a substrate usually a transparent substrate such as glass;
D1 is a first transparent dielectric layer usually a metal oxide and may include one or more transparent dielectric films;
M is an infrared reflective layer usually silver or other noble metal;
P is a primer layer to protect the underlying infrared reflective layer in a reactive plasma;
D2 is a second transparent dielectric film similar to D1; and R is an integer equal to or greater than one and is the number of repetitions of the above layers.
The dielectric layers, D1 and D2, adjust the optical properties of the coating stack. These layers also provide some physical and chemical protection to the fragile infrared reflective layer(s) which are usually silver layer(s). Unfortunately, many process-friendly and cost-effective dielectric materials are often susceptible to abrasion and corrosion as well. For example, zinc oxide e.g., as disclosed in U.S. Pat. No. 5,296,302, which usually forms a crystalline film, is susceptible to attack by acids and bases; bismuth oxide, which usually forms an amorphous film, is soluble in certain acids; tin oxide, which usually forms an amorphous film, is susceptible to attack in certain basic environments.
To reduce corrosion, some Low-E coating stacks have an overlaying protective overcoat of a chemically resistant dielectric layer. This layer preferably has desirable optical properties, manageable sputter deposition characteristics, and is compatible with other materials of the coating stack. The titanium dioxide films disclosed in U.S. Pat. Nos. 4,716,086 and 4,786,563 are protective films having the above qualities. There are other chemically resistant materials that have limitations, e.g., are more challenging to sputter. Silicon oxide disclosed in Canadian Patent No. 2,156,571, aluminum oxide and silicon nitride disclosed in U.S. Pat. Nos. 5,425,861; 5,344,718; 5,376,455; 5,584,902 and 5,532,180 and in PCT International Publication No. WO 95/29883 are examples of such materials. New sputtering deposition techniques in recent years, e.g., cylindrical magnetrons and dual planar magnetrons, have made the deposition of nitrides and oxides of silicon more practical. As a result of such new sputtering techniques, Low-E coating stacks with silicon nitride as one, or all, of the dielectric layers (D), and without additional protective overcoats, have been disclosed e.g. in U.S. Pat. Nos. 5,563,734 and 5,514,476.
In the instance where a protective layer or dielectric layer includes silicon, the cathode used in the sputtering process usually includes an alloy element to facilitate sputtering the silicon cathode. An alloying element used is aluminum, while other elements, e.g., boron and some transition metals, have also been used. U.S. Pat. No. 5,417,827 discloses a silicon nickel alloy. Although silicon nitride is chemically durable, the nitrides of the alloying element which may be present in the coating layer may not show the same level of durability e.g., aluminum nitride decomposes in hot water to form a hydroxide of aluminum.
As can now be appreciated, the above patents/patent applications disclose various protective layers or films to protect underlying coating layers and/or films; however, as was discussed, the presently available protective layers or films have limitations and/or drawbacks. It would be advantageous, therefore, to provide additional protective layers or films to protect underlying coating layers and/or films that minimize if not eliminate the limitations and/or drawbacks of the presently available protective layers.
This invention relates to an improved coated article having a functional coating on a substrate and a protective layer over the functional coating. The improvement is a protective layer of silicon oxynitride or silicon aluminum oxynitride. The protective layer of the instant invention may be homogeneous, graded or non-homogeneous, each term is defined herein. The protective layer of the instant invention may be the last layer or film deposited on a coating stack or a film under the last layer or film deposited.
The invention further relates to the method of depositing the protective layer.